1. Field of the Invention
The present invention relates to a fluid powered apparatus that has application for clamping, punching, welding and other functions that are necessary in the manufacture and assembly of machines and vehicles such as automobiles. More particularly, the invention is related to a dual action fluid powered apparatus designed to implement a rapid movement in approaching a workpiece until contact is effected. The movement of the apparatus upon contact with the workpiece is then transformed to a slow, more powerful working mode. Specifically, the invention is a device which monitors the load applied to a workpiece.
2. Description of the Prior Art
The prior art reveals a wide variety of fluid powered devices that employ a plurality of cylinder and piston combinations to control the speed and force of the device as an element thereof advances toward a workpiece.
In general, most of the prior art devices utilize a tandem arrangement for the various pistons that are all contained within a single cylindrical housing.
By way of example, the present invention differs from the oleopneumatic jack that is shown and described in U.S. Pat. No. 3,426,530 entitled "Oleopneumatic Jack with Staged Structure" issued Feb. 11, 1969, to Alexander Georgelin. The jack has a cylindrical tubular body structure with end caps attached thereto. A first piston is positioned at one end within the cylindrical body. The piston has attached thereto an elongated hollow plunger that is adapted to move with the piston. A floating piston is positioned so that it slides freely along the previously mentioned hollow plunger. A third piston is positioned near the other end of the cylindrical body. The third piston has coupled thereto, as an integral part, a plunger that protrudes from the other end of the cylindrical body. The third piston contains a hollow central chamber which extends into a portion of an integral attached plunger. Air pressure is applied to one end of the floating piston thus causing it to urge oil against the third piston which in turn causes the plunger attached to the third piston to extend from the cylindrical body. After the initial rapid advancement of the first piston and the attached elongated hollow plunger, air pressure is introduced behind the first piston. As the first piston moves axially along the interior of the cylindrical body, its attached hollow plunger enters the oil filled chamber of the third piston thus causing it to move slowly while exerting a large force.
In U.S. Pat. No. 4,099,436 entitled "Apparatus for Piercing Sheet Material" issued Jul. 11, 1978, to Donald Beneteau, there is described a force intensifier that employs an oil reservoir that is external of a cylindrical structure that contains a pair of pistons in axial alignment. The oil in the reservoir is forced into the cylinder by pressurized air that is in direct contact with the oil. The oil that is introduced into the cylinder moves one of the pistons, causing a tool carrying plunger to advance toward a workpiece. In order to intensify the force delivered by the tool carrying plunger, air is introduced behind the other piston, causing it to move an attached plunger into a constricted cavity where the oil pressure is greatly increased, thereby exerting an even greater force on the tool carrying plunger.
One of the disadvantages of the above described apparatus is that its position cannot be readily changed because of the air-oil interface in the reservoir.
An additional load producing cylinder is shown in FIG. 3 of U.S. Pat. No. 4,395,027 entitled "Pressure Intensifying Device" issued Jul. 26, 1983, to Robert Nordmeyer. FIG. 3 of the above referenced patent depicts a cross-sectional view of a pressure intensifying device that has an essentially cylindrical configuration. There is a first piston and plunger combination that moves in the direction towards a second piston plunger combination. The first piston moves under the influence of air pressure and returns to its original position by the biasing action of a compression spring. The second piston is essentially hollow and is filled with oil that supplies the force that causes the second piston and plunger to move linearly. After the second piston has accomplished its initial movement, the first piston plunger is advanced into the oil filled chamber of the second piston. The force on the second piston is thus intensified. The cylinder contains an internally positioned oil reservoir through which the first piston plunger passes. The just mentioned device utilizes, in tandem, pistons that move in the same direction during the initial or advancement movement. One of the inherent drawbacks of the just described device is its overall length. Then, too, the spring that is biased against the first piston subtracts from the overall load that is applied by air pressure.
The present invention also employs a floating piston, however, its direction of motion is opposite to the floating piston shown in U.S. Pat. No. 3,426,530. Thus, the present invention can accomplish the same function as U.S. Pat. No. 3,426,530 within a smaller space. When large numbers of load intensifiers are utilized in close proximity to one another space is always at a premium.
The present invention does not have an air-oil interface since the oil is contained completely within the confinement of the apparatus. Also, the present invention utilizes a reverse direction floating piston concept to reduce the overall length of the apparatus. The present invention also has a plunger unit that is separate from the load enhancement plunger.
The present invention does not utilize springs to aid in the movement of the pistons. Also, the present invention is not arranged in a continuous linear array as is the device described in U.S. Pat. No. 4,395,027.